Description

This is a small high voltage boost converter that uses an MC34063 buck-boost converter IC.
This µHVPSU can work from 3V up to 6V and generate a voltage from [input]V up to 300V MAX.

Perfect for Nixie tubes, Geiger counters and other sub-deciAmp applications

μHVPSU v2.0

[Yet to be written :) ]

Don't forget to like the project if you, well, like the project ^^
If you want to get notified of the future project logs, or if you are interested, or if you want to do me a favor, you can follow this project to see the logs & changes in your personal feed !!

Details

I was playing around with Nixie tubes, and I was using a 10$ HV supply kit on eBay to generate the 200VDC needed to power them.

My friend Manoel (@M.daSilva) uses an assembled module, which also costs 10-12$. It's a reasonable price, but I don't really understand why it's "so" expensive when you see the few components on it.

A few months later, I found a quite interesting website (link) made by Radu Motisan (Hackaday.io profile), which has a lot of projects involving High Voltage radio tubes, geiger tubes, etc.

I came across a post with a really small HV boost converter, powered by a CR2025 battery (link).

This gave me the idea to make my own; the micro High Voltage Power Supply, or µHVPSU, for short.

My goal here is to make a small HV PSU that costs less than 5$, "labor" included.

The schematic is nearly entirely based on the one on the website, but I made some modifications (see project log 1)

Project progression : about 75%

If this project works, I will put a link somewhere where you will be able to buy the PCB directly on DirtyPCBs.

P.S.: I misread the MMBTA42 datasheet, so the maximum input voltage drops from 16V to 6V. For the next revision (V1.1) I'll probably use the STR1550, as V(eb) is equal to 9V, and the maximum V(eb) is 500V, which means that the maximum output voltage of the µHVPSU will be 500V !!

Project Logs

For v1.0 of the µHVPSU, I blindly followed an existing schematic of a similar design, that worked (or at least seemed to). So I ordered my PCBs and parts, assembled one, and it didn't work. So I assembled a second one, being extra careful, and it didn't work either. I got so annoyed about it that I decided to shelve this project. Until now !

After hunting on eBay for Nixie tubes, I stumbled on many nixie clock kits and PCBs, with documentation, and most importantly, a schematic. What was really redundant was the use an analog input pin and a PWM output pin of the main µC as the mais DC-DC step-up converter. So I decided to base my new design on one of these schematics.

Here's what I'm talking about :

This particular clock kit uses a PIC microcontroller, which is fine, but it's a bit too much of an overkill for this project.

Instead, I will use an ATTiny44 as they are widely available on eBay at a cheap price (about 6$ for a pack of 10), and they allow me to program them with the Arduino IDE, which I'm already really familiar with ^^ So that gives me a lot more flexibility.

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So yeah, that's it for this log ^^ I'll post again when I have something interesting to say, or when all the new components have arrived :)

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P.S.: M.daSilva and I have decided to make a spreadsheet, in which all of our Nixie tube types and quantities are listed; we have gathered a total of more that 600 tubes (400+ if you don't count the IN-3's)

I made a document for the BOM which I will update a lot while I'm ordering, assembling and testing the µHVPSU. So in order for you to always have the latest file, I made a shared Keynote document, which you can find here.

That's all ^^

N.B.: Why a Keynote document instead of excel or something else ? Well I use the Apple "iWork" and "iCloud" environnement a lot and I'm really comfortable with that (yes you can say I'm a fanboy, yes..). Oh yes also, sorry for the adfly link ¯\_(ツ)_/¯

I want all the components to be on the same side, so it's more convenient to solder by hand (as everything is SMD). It's also better if I want to use that module in future designs.

For all the "Low voltage" components, I used 0603 components. They can be tricky to solder by hand, but it's doable. For the high voltage 10nF onboard cap, I used 1206 size (because I had no choice). I may have to use an externah HV electrolythic capacitor, as 10nF may not be enough.

For the transistors I used SOT-23 types. The PNP transistor is a S8550 general purpose transistor, and the High voltage switching transistor is an MMBTA42 300V transistor (the best I found with a great voltage/current ratio), and it's also why the µHVPSU v1 is limited to 300V.

The rectifier diode of the converter is a HER108, because, reasons.. (Okay, it's the one used in the original design).

Here are some pictures :

(3D renderings made with this tool (don't pay attention to the green color, the real ones will be white))

As said in the project details, I based my schematic on the one on this website (link). Here's the said schematic, so you don't have to leave this page ;)

However, I changed a few things in my design.

First of all, I used classic 4pin-connector_type-breadboard-friendly-type-thingy to interface the module, so it is easier to implement in other designs.

Secondly, I changed the feedback loop system. In the schematic above, there are fixed resistors, which give the module a fixed (theoretical) output voltage of approx. 370VDC. In my design there is an interface pin where you put a resistor between that pin and the HV output, so you can always control the output voltage.

Oh BTW, here's the formula to calculate the output voltage (found on the MC34063 datasheet)

In my design (I hate saying that, but anyway) R1 is has a fixed value of 1k. You can choose the value of R2 by putting a resistor between the "HV+" pin and the "Sense" pin.

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Did you ever get this working? 100mA @ 300V is 30watt. So if powering this at 3 volts then you'd need 10Amps (12-13 if considering losses) input to it. At those kind of current and power levels most parts on the board will not be happy and will not do a particulary good job....